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  1. #14
    Join Date
    Feb 2010
    Location
    The midwest.
    Posts
    663
    Quote Originally Posted by hfjeff View Post
    OK-had the tech back out and here is what was done. He explained to me that when in "cold mode" the furnace basically has 2 fan settings: 1 low "maintain speed" and 1 high "cool down speed." When the system was installed they set the cool down speed to 875 cfm. Then when I had him come out the first time he switched the dip switch to 1050cfm. This past Friday we had the air off and the windows open. It got to 80 deg in the house so we shut the windows and started the air (1pm). By 7pm it was still 79 deg in the house and the A/C had run the entire 6 hours. Since it still did not cool the house, he now set the dip switch to 1400cfm. He told me it is set to match a 4 ton A/C unit and mine is a 2.5 ton. Is he adjusting this correctly? The air is really moving now on the cooldown mode, but is this truly how the variable speed is supposed to work? He did adjust freon and measure output temp of the duct coil and it is 54 deg. It is cool here today so I can't test it.
    Something is wrong. He shouldn't have to set the airflow to 1400cfm. I bet your short on return air in the house.

  2. #15
    Join Date
    May 2010
    Location
    SF Bay Area, CA
    Posts
    390
    Setting your 2.5T a/c to 1400 CFM doesn't sound right at all.

    What is the output temp at your supply registers? It sounds to me that the new install may have caused some supply duct leaks so the 54* air at the coil isn't getting to where it needs to be.

    You mention low and high speeds. Is your A/C a multi-stage system?

  3. #16
    Join Date
    Feb 2010
    Location
    The midwest.
    Posts
    663
    Quote Originally Posted by drewski11 View Post
    Setting your 2.5T a/c to 1400 CFM doesn't sound right at all.

    What is the output temp at your supply registers? It sounds to me that the new install may have caused some supply duct leaks so the 54* air at the coil isn't getting to where it needs to be.

    You mention low and high speeds. Is your A/C a multi-stage system?
    With the old Lennox Pulse, it wouldn't be a 2-stage A/C.

  4. #17
    Join Date
    Jun 2006
    Location
    Richmond, VA
    Posts
    2,912
    Let me see if I understand the facts.....

    1. The only thing you had changed was the furnace?
    2. You have the same AC as before?
    3. 1000cfm is the correct setting for a 2.5 ton....did you insist that your old furnace blew harder and he set it up to 1400 to appease you?
    4. I have to ask....since you had such a newer thermostat-did you tell the contractor you wanted to keep it?

    I don't know what the temp and humidity conditions were at the time you were expecting the temp to drop quickly, in my area the temp and humidity has been so high, it will take forever if the windows have been left open any amount of time. In cooling, all the furnace does is blow the air. With the varible speed blower you can actually set what it needs to be.

  5. #18
    Join Date
    Aug 2010
    Posts
    8
    I definitely do have more air "feeds" than "returns". 3 bathrooms upstairs have no returns, and I did block off a few as the installer told me that if the system felt a vaccuum on the return, the fan would ramp up. Not. So I have removed the blocks on the returns.

    * The old Lennox pulse was not multi-stage, just on off.
    * The A/C unit is the same- a 5 year old Lennox 2.5t
    * The t-stat is the same - a generic Aprilaire digital programmable
    * He probably did bump up the speed to appease me because I am calling him and complaining. But as I mentioned, after running for 6 hours and the outside temp had fallen, it was still 79 deg in the house at 7pm-nearly hotter than it was outside.
    * I did not request to keep the thermostat. I asked about a new one and they said I did not need it.
    * How do I control the variable speed blower? They have jumpers set on the motherboard.

    I don't know what the old Lennox furnace is set at as it is gone. I may be able to find out though.

    I do have a a very open concept ranch which is relatively large and old with original windows and modest insulation so it is an uphill battle to heat and cool this place. I just want to make sure this furnace is setup correctly and working the most efficiently as it should.

  6. #19
    Join Date
    Jun 2006
    Location
    Richmond, VA
    Posts
    2,912
    If I understand correctly you have 54 degree air coming out after the furnace change. Roughly that is all the AC can do. Upping the cfm to 1400 will give it more capacity for sensible heat.

    Did the AC do the same before the change out of the furnace?

  7. #20
    Join Date
    Aug 2010
    Posts
    8

    1400CFM is working

    It was 90 here today and the A/C is working well and actually took a break now and then. With the fan jacked up to 1400CFM, it seems to be working as the old Lennox did with about 52% humidity. I called another contractor for some advice and he stands behind my installing contractor as a good group of techs. He talked to me for about a half hour to discuss possible causes. We have come to the conclusion that I may need a few more ducts added as I believe my whole problem to this point may have been air flow. Maybe my old Lennox was jacked up as well to complensate for too few ducts. Thanks for all of the advice and help.

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